Using reverse engineering (following tracks), we have mapped the design of a MBC5 Cart with sram and battery.
With this info we have made a schematic of the cart, and the PCB design of the cart with a flash chip, MBC5, 32Kbit RAM and up to 32Mbit ROM.
Eagle files : cartucho_flash_15-06-2008.zip
We have sent this pcb to a manufacturing service, is some days we'll update with the results.